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Assessment of tissue perfusion and vascular function in mice by scanning laser Doppler perfusion imaging
摘要： Post-occlusive reactive hyperemia (PORH) is a key feature of physiological vasomotion to appropriately match the supply/demand ratio of tissues. This adaptive mechanism is severely disturbed in endothelial dysfunction with a reduced flow-mediated dilation (FMD). Reduced PORH and FMD are powerful prognostic risk factors in cardiovascular disease. While these parameters are frequently determined in human beings, comparable methods applicable to mouse models are sparse. We aimed to evaluate the applicability and accuracy of scanning laser Doppler perfusion imaging (LDPI) to measure PORH in the mouse hindlimb. Changes in mean perfusion in response to vasoactive drugs and PORH (assessed by scanning LDPI) were compared with changes in diameter and blood flow in the femoral artery, as assessed by high-resolution ultrasound. We found that the measured LDPI signal significantly correlated with changes of inflow into the femoral artery. Vasodilation induced by administration of nitroglycerine and acetylcholine increased vessel diameter, blood flow and mean perfusion, while vasoconstriction following administration of epinephrine decreased all three parameters. PORH was induced by temporal occlusion of the femoral artery with an external cuff. During occlusion, mean perfusion decreased to a condition of zero-perfusion and release of the cuff induced an immediate increase in blood flow that was followed by femoral artery dilation driving PORH/ perfusion. Surgical removal of the femoral artery decreased mean perfusion to a zero-perfusion level and fully abolished PORH. Importantly, the measurement of the PORH response by scanning LDPI is highly reproducible as determined by repeated measurements and intra/interobserver variation analysis. Last, we found that the PORH response was dependent on nitric oxide synthase and cyclooxygenase and declined with age. Thus, we here provide novel and robust non-invasive methods to serially measure tissue perfusion at baseline and during physiological and pharmacological modulation of vasomotor tone in the hindlimb of mice. The application of these LDPI scanning and ultrasound-based methods may be useful for testing the effects of drugs affecting vasomotor function or future elucidation of mechanisms leading to vasomotor dysfunction in mice in vivo.
关键词： age-dependent endothelial dysfunction,Laser Doppler perfusion imaging,nitric oxide synthase,hindlimb,reactive hyperemia
更新于2025-09-19 17:13:59
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Measurement of Loudspeakers with a Laser Doppler Vibrometer and the Exponential Sine Sweep Excitation Technique
摘要： This paper presents an experimental study of vibrations of the cone of loudspeakers. Measurements of the axial acceleration have been performed in hundreds of points on the surface of the cone employing a Laser Doppler Vibrometer and using the exponential sine sweep excitation signal. The recorded signal has been transformed into an impulse response by convolution with the matched inverse sweep signal. From the knowledge of the acceleration in each point of the radiating surface, the free field sound pressure in axis at 1 m distance has been computed. The research focuses on obtaining results comparable to FEM simulations based only on the linear mechanical behavior of the loudspeaker cone and avoiding any acoustic interference. Moreover, comparing the laser measurements of many samples, the authors seek to evaluate the influence of known variations in the loudspeaker components or production process on the final performances of the device. Post-processing of experimental results is carried out employing a Matlab script, which also computes operational deflection shapes of the loudspeaker cone.
关键词： loudspeaker vibrations,exponential sine sweep,accumulated acceleration level,sound pressure level,Laser Doppler Vibrometer
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE International Ultrasonics Symposium (IUS) - Glasgow, United Kingdom (2019.10.6-2019.10.9)] 2019 IEEE International Ultrasonics Symposium (IUS) - Non-Contact laser ultrasound (N-CLUS) system for medical imaging and elastography
摘要： MIT Lincoln Laboratory, the Medical Device Realization Center (MEDRC) at MIT, and the Massachusetts General Hospital (MGH) are collaboratively developing a novel optical system that acquires ultrasound images within the human body without physical contact to the patient. The system is termed, non-contact laser ultrasound (N-CLUS) and yields anatomical images in tissue and bone and can also measure elastographic properties, in-vivo, all from an operational standoff of a few inches to several meters as desired. N-CLUS employs a pulsed laser that converts optical energy into ultrasonic waves at the skin surface via photoacoustic mechanisms, while, a laser Doppler vibrometer measures reflected-emerging ultrasonic waves from tissue at depth at the skin surface. The key of the N-CLUS approach is driven by shallow optical absorptivity that creates an acoustic source that enables ultrasound propagation deeper into the tissue. We discuss the motivation of the non-contact laser concept, its development path involving signal generation, skin and eye safe laser measurement, and system design perspectives. Elastogrphic measurements are then demonstrated with determination of bone elastic moduli for beef rib within tissue. N-CLUS images from soft tissue specimens are also compared with commercial ultrasound, showing that the noncontact optical approach may have potential as a viable method in medical ultrasound.
关键词： laser Doppler vibrometry,photoacoustics,non-contact laser ultrasound,medical ultrasound imaging,elastography
更新于2025-09-16 10:30:52
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Heterodynes Laser-Doppler-Vibrometer mit gekoppelten Diodenlasern zur Schwingungsanalyse von SAW-Filtern / Heterodyne laser-Doppler vibrometer with frequency-offset-locked diode lasers for vibration analysis of SAW filters
摘要： Heterodyne interferometers measure vibration amplitudes at frequencies > 100 MHz with defined measurement uncertainty in contrast to homodyne methods. The low efficieny of Bragg cells for frequency shifting > 409 MHz impedes the application of heterodyne interferometers for the Gigahertz range. In this paper, we present an automated measurement system for the aquisition of operting deflection shapes of microsystems with a laser-Doppler-vibrometer microscope, in which an optical phase-lock loop controls the frequency offset of two diode lasers and, therefore, determines the carrier frequency. Our measurement system provides a vibration-amplitude resolution in the picometer range for vibration frequencies from 10 MHz to 700 MHz. The measurement capability for the absolute amplitude and phase of the vibration is exemplary shown with a vibration analysis of a surface-acoustic-wave filter.
关键词： MEMS testing,heterodyne laser-Doppler vibrometry,Heterodyne interferometry,phase-locked loop
更新于2025-09-16 10:30:52
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Laser Doppler blood flowmeter as a useful instrument for the early detection of lower extremity peripheral arterial disease in hemodialysis patients: an observational study
摘要： Background: A simpler method for detecting atherosclerosis obliterans is required in the clinical setting. Laser Doppler flowmetry (LDF) is easy to perform and can accurately detect deterioration in skin perfusion. We performed LDF for hemodialysis patients to determine the correlations between blood flow in the lower limbs and peripheral arterial disease (PAD). Methods: This retrospective study included 128 hemodialysis patients. Patients were categorized into the non-PAD group (n = 106) and PAD group (n = 22), 14 early stage PAD patients were included in the PAD group. We conducted LDF for the plantar area and dorsal area of the foot and examined skin perfusion pressure (SPP) during dialysis. Results: SPP-Dorsal Area values were 82.1 ± 22.0 mmHg in the non-PAD, and 59.1 ± 20.3 mmHg in PAD group, respectively (p < 0.05). The LDF-Plantar blood flow (Qb) values were 32.7 ± 15.5 mL/min in non-PAD group and 21.5 ± 11.3 mL/min in PAD group (p < 0.001). A total of 21 non-PAD patients underwent LDF before and during dialysis. The LDF-Plantar-Qb values were 36.5 ± 17.6 mL/min before dialysis and 29.6 ± 17.7 mL/min after dialysis (p < 0.05). We adjusted SPP and LDF for PAD using logistic regression, SPP-Dorsal-Area and LDF-P were significantly correlated with PAD (p < 0.05). The receiver-operating characteristic curve analysis indicated cut-off values of 20.0 mL/min for LDF-Plantar-Qb during dialysis. Conclusion: LDF is a simple technique for sensitive detection of early-stage PAD. This assessment will help physicians identify early-stage PAD, including Fontaine stage II in clinical practice, thereby allowing prompt treatment.
关键词： Skin perfusion pressure,Peripheral arterial disease,Laser doppler flowmetry
更新于2025-09-16 10:30:52
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XXX. Messtechnisches Symposium || Modellierung der Aufl?sungssteigerung mittels photochromer Schichten für die nanoskopische Laser-Doppler-Vibrometrie
摘要： Es wird ein Modell zur Simulation der reversibel schaltbaren Absorption in einer photochromen Schicht, die sich im Kontakt mit dem Messobjekt befindet, für die Aufl?sungssteigerung in der Laser-Doppler-Vibrometrie vorgestellt. Das Modell umfasst den photochemischen Prozess in den eingebetteten, photochromen Molekülen unter komplexer Bestrahlung sowie die Reflektion an der Messoberfl?che. Mit Hilfe der Simulationen kann das Design eines nanoskopischen Laser-Doppler-Vibrometers überprüft und optimiert werden. Im Modell werden Beugungseffekte sowie Streuung vernachl?ssigt. Unter diesen Voraussetzungen wird gezeigt, dass das Potential für eine laterale Aufl?sungssteigerung auf λ/10 gegeben ist.
关键词： Nanoskopie,Photochromie,Laser-Doppler-Vibrometrie
更新于2025-09-16 10:30:52
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Minimally invasive laser Doppler flowmetry is suitable for serial bone perfusion measurements in mice
摘要： In vivo laser Doppler flowmetry (LDF) has previously been used to quantify blood perfusion accurately at a single timepoint in the murine tibial metaphysis. However, this procedure entailed substantial disruption to soft tissues overlying the bone and caused notable localized inflammation for several weeks after the procedure, impeding serial measurements in the same mouse. In this study, we tested a less invasive technique to measure perfusion in the tibia with LDF and determined that it can be used serially in the same mouse without causing signs of inflammation or gait perturbations. Twenty 14-week-old C57Bl/6J mice were evenly divided into groups that either had daily treadmill exercise or remained sedentary. Within these activity groups, mice were evenly subdivided into groups that received LDF measurements either weekly or only once at the study endpoint. Bone perfusion was measured with LDF in the anteromedial region of the right tibial metaphysis. Serum concentrations of interleukin 6, incision site wound area, and interlimb coordination during gait were measured weekly for four weeks. Tibial perfusion did not differ significantly between exercise and sedentary groups within the weekly or endpoint-only LDF groups at any timepoint. Perfusion was significantly increased in the third week in the weekly LDF group relative to measurements in the second and fourth weeks. Ligation of the femoral artery caused consistent, rapid reductions in tibial perfusion, validating that LDF is sensitive to changes in tibial blood supply. Weekly LDF procedures did not adversely affect gait, as interlimb coordination during treadmill locomotion was similar between weekly and endpoint-only LDF groups at every timepoint. Images of the incision site show wound closure within one week, and serum concentrations of interleukin 6 were not significantly different between weekly and endpoint-only groups. Together, these findings demonstrate that our minimally invasive LDF technique is suitable for serial in vivo measurements of intraosseous blood perfusion without inducing localized inflammation or negatively affecting gait patterns in mice.
关键词： Laser Doppler flowmetry,Vascular supply,Serial measurement,In vivo,Bone blood perfusion,Minimally invasive
更新于2025-09-16 10:30:52
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Laser-Doppler-Vibrometrie an dynamischen Strukturen von Windenergieanlagen
摘要： Numerous issues in the design, construction and operation of wind turbines require vibration measurements, especially on rotor blades under operating conditions. Built-in sensors can only perform this task selectively, externally mounted sensors only with great effort and possible influence on the object to be measured. A system-independent, distant measuring method will be presented here: the combination of a laser Doppler vibrometer with a method for tracking the rotation of the rotor. It requires a separation of the effects caused by the macroscopic movement of the rotor from the real vibration movements. One is the Doppler effect of the fast rotor movement, additionally, the signal noise of the backscattered coherent laser radiation and motion artifacts due to the oblique viewing angle are discussed. First test measurements demonstrated the applicability of the method despite these challenges.
关键词： tracking method,wind turbine,Laser Doppler vibrometry,heterodyne detection,rotor blade
更新于2025-09-16 10:30:52
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Application of a laser-Doppler anemometry for the study of unsteady flow structure in a model micro-hydro turbine
摘要： Current work deals with an LDA characterization of the velocity distributions and pressure pulsation maps in an axisymmetric draft tube for the flow conditions corresponding to wide range of the operating regimes of the micro-hydro turbine unit. For the detailed analysis of the velocity profiles, three characteristic regimes corresponding to part-load regime with precessing vortex core formation, best efficiency regime and overload regime of hydro turbine operation were selected. To capture spatial characteristics of the unsteady flow for part-load regime a phase averaging procedure for the LDA data has been employed.
关键词： phase averaging,micro-hydro turbine,laser-Doppler anemometry,precessing vortex core,unsteady flow structure
更新于2025-09-16 10:30:52
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Mechanical Energy Dissipation Through the Ossicular Chain and Inner Ear Using Laser Doppler Vibrometer Measurement of Round Window Velocity
摘要： Human hearing is predicated on the mechanical transfer of acoustic vibration from the tympanic membrane through the ossicular chain to the inner ear. The sound is only successfully conducted into a neurological signal with movement of cochlear hair cells which occurs with displacement of cochlear fluid. In order for this displacement to occur optimally, not only must there be an intact ossicular chain but also a compliant and intact round window membrane which must vibrate in opposite phase of the acoustic vibrations entering the cochlea through the stapes at the oval window (1,2). This mechanical transfer of acoustic vibration from the tympanic membrane to the inner ear can be conceptualized with the transfer function. Traditionally the transfer function with respect to auditory signal transmission has been evaluated by relating sound pressure level or decibels at the tympanic membrane to velocity of stapes footplate movement defined by the equation H ? Vstapes/Pec (3). While a number of studies have independently examined the fundamental response of the ossicular chain and the round window to an acoustic stimulus independently of each other, there have not been any studies which directly evaluate the transfer function of the middle ear by directly comparing ossicular chain with round window velocity and transfer function as the primary output variable (4–7). If the round window physiology can be more fully characterized, particularly in relation to stapes footplate displacement and transfer function, it would lend itself to usage as a more accurate proxy for transfer function into the inner ear in contrast to stapes footplate displacement.
关键词： Laser Doppler vibrometer—Mechanical energy transmission—Ossicles—Round window.
更新于2025-09-16 10:30:52